Various elastic composites have been formed by bonding an elastic polymer layer in the form of a film, foam, nonwoven web or parallel strands, to one or more nonwoven facing layers. A “stretch bonded laminate” (“SBL”) is any laminate in which an elastic layer is bonded to one or more facing layers while the elastic layer is stretched. When the elastic layer is subsequently relaxed, gathers form in the facing layer(s). Stretch-bonded laminates are described, for instance, in U.S. Pat. No. 6,387,471 to Taylor et al., and U.S. Pat. No. 6,323,389 to Thomas et al., which are incorporated herein by reference. A “neck-bonded laminate” (“NBL”) is any laminate where an elastic layer is bonded to one or two non-elastic facing layers while the elastic layer is relaxed and the facing layer(s) are extended or necked to reduce their dimensions in the direction orthogonal to the extension. Neck-bonded laminates have cross-directional stretch and recovery properties. Neck-bonded laminates are described, for instance, in U.S. Pat. No. 5,853,881 to Estey et al., U.S. Pat. No. 4,965,122 to Morman, and U.S. Pat. No. 6,001,460 to Morman et al., and U.S. Pat. No. 5,789,065 to Haffner et al., which are incorporated herein by reference. A “neck-stretch bonded laminate” (“NSBL”) is any laminate where an elastic layer is bonded to one or two facing layers while the elastic layer is stretched, and the facing layer(s) are extended in the same direction to cause necking in the direction orthogonal to the extension. Thus, a NSBL has features common to both a SBL and a NBL.
A “vertical filament laminate” (“VFL”) or a “vertical filament stretch bonded laminate (“VFSBL”) is any laminate where an elastic layer of substantially parallel, non-intersecting elastic strands formed of an elastomeric material is bonded to one or two facing layers while the elastic strands are in a stretched state and the facing layers are not stretched. When the laminate is relaxed, the elastic strands retract and the laminate becomes somewhat puckered and corrugated. The VFL exhibits elastic stretch in the longitudinal direction of the elastic strands which is also the machine direction of the inelastic facing layer or layers. A “continuous filament stretch bonded laminate” (“CFSBL”) is any laminate where an elastic layer formed of substantially parallel, non-intersecting elastic strands overlaid by at least one overlapping array of conventional meltblown fibers is bonded to one or two facing layers while the elastic layer is stretched in the machine direction. Both the parallel elastic strands and the conventional meltblown fibers are formed of an elastomeric material. When the CFSBL is allowed to retract to a relaxed state, some gathering forms in the facing layer or layers. The relaxed CFSBL can be stretched in the machined direction of the laminate. Continuous filament stretch bonded laminates are disclosed, for instance, in U.S. Pat. No. 5,385,775 to Wright.
Various thermoplastic elastomers are known for use in the elastic layer, including without limitation styrenic block copolymers. For instance, U.S. Pat. No. 6,323,389 to Thomas et al. discloses the use of block copolymers having the general formula A-B-A′ or A-B, wherein A and A′ are each a thermoplastic polymer end block which contains a styrenic moiety such as a poly(vinylarene) and B is an elastomeric polymer midblock such as a conjugated diene or a lower alkene polymer. The A and A′ blocks may be formed of the same or different polymer segments. Tetrablock copolymers having the formula A-B-A-B are also disclosed, where A is a thermoplastic polymer block as described above, and each B is an isoprene segment hydrogenated substantially to a poly(ethylene-propylene) segment.
Elastic laminates are typically the most expensive component in personal care products such as diapers, diaper pants, adult incontinence garments, feminine hygiene products and the like. Important properties of elastic laminates include providing sufficient elastic tension at various degrees of elongation during use, and providing sufficient recovery upon stress relaxation (creep resistance).
There is a further need or desire for apparatus and methods for making elastic laminates which perform better at lower cost.